Automatic tuning control circuit



Nov. 2, 1948. H. c. TITTLE 2,452,878

AUTOMATIC TUNING CONTROL CIRCUIT Filed Feb.\,8, 1944 Patented Nov. 2, 1594-8 AUTOMATIC TUNING CONTROL CIRCUIT Hulburt C. Tittle, Cheektowaga, N. Y., assignor to Colonial Radio Corporation, Buffalo, N. Y.

Application February 8, 1944, Serial No. 521,512

(Cl. Z50- 40) 9 Claims.

This invention relates to an automatic tuning control circuit, and more particularly to automatic crystal controlled radio transmitters or receivers, although it will be understood that my invention may be applied in other apparatus where automatic tuning of a cir-cuit to any one of a series of predetermined frequencies is desired.

Various forms of circuits of this type have been described and claimed in a co-pending application of William S. Wineld, Serial No. 463,775, led October 29,1942. In apparatus of this type, the circuits are automatically tuned to desired frequencies determined by crystals, and do not involve the setting of mechani-cal elements, such' as pins, contactors, selecting cams, rocker bars, or the like.

In experimental work With apparatus such as that described in the above application, it has been found that, while the system described operates as contemplated when the resonance curves of the cir-cuits controlled are separated or do not overlap to any considerable extent, diiculties may be encountered when the channels desired to be tuned are so close to each other that the resonance curves overlap to a considerable extent. Under such conditions the apparatus, when tuned to one frequency, may remain tuned to that frequency although the controls are operated to change the frequency.

It is an object oi this invention to provide appal ratus of the class described in which these difculties are eliminated and reliability of operation is assured, even though a number of channels are provided so closely adjacent in frequency that the resonance curves of the apparatus for various channels overlap.

It is a further object of my invention to provide apparatus which will be closely tuned to the desired channel even though other channels are closely adjacent to the desired channel.

It is a still further object of my invention to provide improved apparatus of the class described having improved operational characteristics such that the apparatus will function and tune properly even where channels are as closely spaced as tuning selectivity permits.

Still other objects and advantages of my invention Will be apparent from the specification,

In the drawing.

Fig. 1 is a circuit diagram of automatic tuning A apparatus of the type to which my invention is applied.

Fig. 2 isa curve illustrating the operation of such apparatus.

Fig. 3 is a curve illustrating conditions when the apparatus is required to tune to one of a number of closely spaced channels.

Fig. 4 is a circuit diagram of apparatus in accordance with my invention.

Referring now more particularly to Figs. 1 and 2, reference numeral 2 designates a variable tuning instrumentality such as a variable condenser, variometer, or the like, driven by a suitable operating means, such as motor 3, through a suitable reduction gearing, and servingto tune one or more controlling circuits, which may be oscillator circuits, antenna circuits, or, in fact, any tunable circuit required to be tuned and containing inductance (not shown), as well known in the art, with which tuning instrumentality 2 cooperates.

The tuning instrumentality, which, for sake of simplicity, is referred to as a condenser, although it may be another instrumentality, may be a single or gang condenser, and may tune one or more circuits, as may be desired, where two or more circuits are desired to be simultaneously tuned. The tuning instrumentality is arranged for continuous rotation; i. e., no stop is provided limiting its rotation to 180 as is sometimes used in condensers. For purposes of simplicity, the remainder of the tuning circuit or circuits is not shown, but a rectified voltage derived from the circuit by means of anyV suitable rectiiier known in the art as in Figure l may be impressed through terminals l between the cathode 6a and control electrode Eb of a relay control tube 6. Connected to the anode 6c there may be provided a relay 1, Whose circuit may be completed to the +B sour-ce, the negative terminal of which is connected to cathode Ba. The relay winding 'l controls relay contacts 'la and 1b in such a manner that when plate current of a predetermined value iiows through relay l', contacts 'la and 'I b are closed, thereby energizing the motor 3 through suitable power source 9.

A suitable source of biasing voltage 5 may be provided in the grid circuit of tube 6 if desired for the purpose of more exactly determining the operating characteristics of the tube 6.

The characteristics of tube 6 and its bias are so chosen that when the voltage impressed between terminals 4 is zero, the space current of tube 6 is more than enough to maintain contacts la and lb closed.y As the voltage across terminals 4 increases in such a directionas Vto make the grid more negative (El Fig. 2) with respect to the cathode of tube 6, the plate current drops to such a value that the plate current of the tube 6 is insufficient to maintain relay contacts 'la and 'lb in closed position and those contacts open. For any value which maintains the grid more negative than this, the motor circuit will be open and the tuning instrumentality will remain in position.

If the grid 6b of tube 6 becomes less negative than this value, the plate current through tube 6 increases, relay 1 closes, the motor circuit is energized, and the tuning instrumentality isrotated, and this rotation will continue until a voltage sucient to cause opening of the relay 1 is again impressed upon the tube 6.

In operation, assuming that the apparatus is arranged to control the tuning of va transmitter, the operator may have a channel .selecting switch I5, by the operation of which he can connect into the tuned circuit a crystal such as crystals I6, Il,

I8 for each frequency to be tuned. Assuming-that" the apparatus is tuned to a particular frequency as determined by crystal I6, for example and the operator operates the channel selecting switch l for asecondchannelhaving a'diierent frequency, this disconnects the crystal ltunedtoth'e first channel, which-may be called channel A, and-con nectsanother` crystal such as I1 tuned to the new channel, which may be channel B. Assuming that f the newv frequency selected, at which time thevoltage impressed upon tube'willbegin'to risein a negative direction, following thegeneral form of the resonance curve as shown in Fig..2, wherein ordinates represent grid voltage and' abscissae angular movement of the tuning condenser.

Nothing occurs untilthe .grid voltage reaches the magnitude EL 'at which 'pointthe current in Arelay 1 has decreased sufficiently to permit contacts 'la and 'Ib't'o open. As will be understood, the motor will'not instantaneously'stop rotating'butwill coast vto a, stop, the'time required Abeing dependent'upon theinertia of the rotating system, "theloadupon it, and other factors.

Generally speaking, it will be foundthat some definite angular rotation occurs between the current cut=oif point andthe motor :stopping point, which will be substantrfally'constant `for any given apparatus. This may be measuredandis allowed 'for in selecting the point. El, in such a. manner that motor current cut-off occurs just sufcienty in advance of the attainment of Vfull resonance position by the tuning instrumentality, so that "the coasting carries the circuit to the peak of the resonance curve and the stoppedposition .of the apparatus is substantially as indicated in fEig.-2. A somewhat more complicated condition is encountered when thereare a pluralityof-chanlnels rso closely spaced thatthe resonance curves overlap. This vcondition may be represented in Fig. 3, inwhich A` represents the vresonance'curve :of the apparatus l on channel .AQB the resonance :curve on channel B at arslghtly lower'fre- Iquencythan .that `of channel A, .'an'd C thetresomance fcurveJ .of 'the4 apparatus :on channel C, eslightly higher in'xfrequencyf than lchannel A. i It will be Lobser-ve'd that :these resonance curves ovexflapjBoverlappingA onfone side,- and'-'C yover- 4 lapping at the other, and both B and C overlapping A and each other at the center of A.

Here it should be noted that the voltage level E1 on Fig. 3 represents the gridbias which will cause the relay 'l to open the motor contacts. This may occur at an angular position of the condenser 91. The motor then coasts to a nal position 92.

Although the relay openedfat` a `voltageoi E1 on curve A, a reduction of the negative bias voltage to this value will not be sufficient to cause the relay to close. It may merely cause chat- "tering 'To insure positive closure, the negative Voltageimust be Yreduced still further to a voltage level suchas Ea which is just sumcient to cause the relay contacts to close. Generally speaking, -the current in 'the relay actuating winding to produce closure is about twice that at which the relay will open; i. e., once closed, the relay will hold in closed position 'with about half the current required'to move itfrom opentdc'losedposition. For the-closing value, or any less negative value of -grid voltage, the motor circuit' will "be closed. 'If resonance curves'A and C-overlapto suchan extent that the negative biasdevelope'd, as indicated-onresonance curveC, is greater than E2 in a 'negative sense, the motor-*'circuitwill not close when the operator moves ithe control switch from-channel A to 'channel C,'the vtuning condenser will Inot be operated, Aand thecircuit will remairrtuned as ifior-channel A, which may be serious Amistuning on 'channel C. The same wouid be'true for any adjacentcharrnelsbetween A and C, for channel B, and for any Achannels between AandB.

I have found that this diiculty can be 'avoided by arranging the'apparatus so-thaton the'selection of a new channel, `the motor circuitiis positively energized and the relay I'l deprived of control of`the motor until'the ymotor hasfcarriedth'e tuning through Athe remaining channels available andstarted another excursion through thechannels; that is to"say,'ii theapparatus'tunes'over a frequency range of '500 vto '1*,600 kc., and happens fto be ltuned to 'TO0-kc., then ifithepperator changes 'the' frequency to A860 "kc., Athe motor will begin to rotate and will tune ltheV apparatus higher 'through 80G kc., and continue up cto --the end of the band, at which Vtime the =tuning cone denser swould continue'to rotate-until'the'tuning reentered loyv the lower end of the band; i. e., 500 kcandibegan another cycle of'tuning. V,This assures that lva new channel must always be approached onrthe same angular'side.

When -the :tuning instrumentality reenters 'the useful tuning arc (begins a new tuning cycle), 'control is 4restored to the relay lfandnormal operation is obtained. Thsiis accomplished by the vapparatus shown in Fig. 4, like Vthat 'in'Fig 1, except in theffollowing respects:

The -apparatusfshown in Fig; 4 has been prol.vided 'with an Vadditional relay A#lV-having an actuating windingconnected in serieswithswitch 'I'I'having'movable contact l la andfixed contact Mb. This rcircuit i-s connected "directiy across the power source 9 so that-wheneverswitchII`is closed, current iicws through the actuating-winding o'f-relay |-ii,-thereby closing ymovablerelay con; tacts ma and lc against the Xed relaycontacts lb 'and''lild' respectively. It'will be noted that 'contactsllla andiib keep the motor circuitclosed independently of relay contacts 'la and` "1b-"of relay-1".

In addition to relay IU, I mayfproviil-efa-cam switch-1'2fcomprisingfcam' disk l"21::"1'navinga'notch 2b adapted to receive the movable cam actuated contact I2C which engages xed contact I2d As shown, the cam switch I2 may be in series with relay contacts Ille and |011 and the branch of the circuit formed by these contacts and by the cam switch in parallel with the manual switch I I.

The cam disk I2 is geared or otherwise connected to the motor 3 in such a manner that the disk I2 makes one complete rotation while the tuning instrumentality is making one revolution.

For example, each time the tuningk condenser A*reaches such a position that the tuned circuit is at its lowest frequency and about to move its frequency upward through the tuning range, the

cam notch IZ'b moves under the cam Contact I2C and the latter falls into the notch and permits the cam switch to open.

With this combination of circuit elements it Y will be seen that when manual switch I I is closed, a circuit is established through the actuating winding-oi relay Iii, thereby closing relay contacts Illa and Ic against fixed contacts Iiib and Illdz When this occurs, the relay It is locked in because the circuit in parallel to switch iI is closed through the actuating winding through contacts Ic and Ind, and the cam switch I2. Manual switch Il may now be opened without aiecting subsequent operation,

It will also be seen that so long as relay I is energized the motor circuit will be closed -through contacts Illa and Iilb and, therefore, the motor will continue to operate as long as cam switch I2 is closed, regardless of the action of contacts 'la and 1b, in response to the plate current of tube Ii, and the motor will continue to operate until the cam switch has rotated to a point corresponding t0 the beginning of the tuning cycle of condenser 2.

At this point cam switch I2 will open, interrupting the holding circuit of relay Ill, and contacts Ia. and Illb and Isc and Id will open due to the interruption of current in the winding of relay I. Control of the motor operation is now restored to the relay 'I, and if the negative voltage impressed on terminals 4 is then suicient to reduce the flow of plate current to the value of -E1, the motor will be stopped just as if addi tional relay i il, manual switch I I, and cam switch lI 2 were not provided.

In short, the eiTect ci the closure of manual switch il isrto positively insure that no matter how many channels there may be to which the apparatus may be tuned, the tuning condenser will move through the uncompleted portion of the cycle in a positively locked condition where it cannot be stopped by the control voltage. When the uncompleted portion of the cycle is completed and the tuning condenser is ready to start another cycle, the lock-in circuit is opened by the operation of the cam switch.

In then foregoing description, it is assumed that the manual switch ll is merely closed momentarily and is thereafter immediately opened. If the switch Il were kept closed, the motor would continue to rotate indeiinitely because the cam' switch would not open the circuit of relay Iii.

To provide against faulty operation in this respect, I prefer to provide switch II in the form of a passing contact on the channel selecting 'f switch or switches in such a way that at any time the operator pushes a button for a new channel, switch I l is momentarily closed to initiate the operation described, and is thereupon immediately opened.

In the specification I have explained the prinf 'estacas ciples of my invention and the best mode in' which I `have contemplated applying those principles so as to distinguish my invention from other inventions, and I have particularly pointed out and distinctly .claimed the part, improvement, or combination which I claim as my invention or discovery.

While I have shown and described a preferred embodiment of my invention, it will be understood that modications and changes may be madev Without departing from the spirit and scope of my invention, as will be apparent to those skilled in the art.

I claim :y

1. In automatic tuning apparatus, in combination, a frequency determining element, a work circuit including a power source for delivering energy limited to a frequency determined-by said element, said work circuit having a variable tuning instrumentality, power means for varying said tuning instrumentality, energy responsive means for interrupting operation of said power means in response to delivery by said work cir-- cuit of a predetermined level of energy,- said last mentioned means being operatively vassociated with said work circuit and means for causing operation of said power means to move said tuning instrumentality through completion of one tuning cycle irrespective of the level of energy delivered by said work circuit.

2. In automatic tuning apparatus, in combination, a frequency determining element, a work circuit including a power source for delivering energy limited to a frequency determined by said element, said work circuit having a variable tuning instrumentality, power means for varying said tuning instrumentality, energy responsive means for interrupting operation of said power means in response to delivery by said Work circuit of a predetermined level of energy, said last mentioned means being operatively associated with said work circuit means for causing operation of said power means, and means for rendering said energy responsive means inoperative through the .completion of one tuning cycle, after the power means is set into operation.

3. In automatic tuning apparatus, in combination, a plurality of frequency determining elements, selecting means for selecting any one of said elements, a work circuit including a power source for delivering energy limited to a frequency determined by the selected element, said work circuit having a variable tuning instrumentality, power means for varying said tuning instrumentality, energy responsive means for interrupting operation of said power means in response to delivery by said work circuit of a predetermined level of energy, said last mentioned means being operatively associated with said work circuit means for causing operation of said power means to move said tuning instrumentality through completion of one tuning cycle irrespective of the level of energy delivered by said work circuit, and means for terminating the operation of said last mentioned means at a predetermined point in` each tuning cycle.

'4.In automatic tuning apparatus, in combination, a plurality of frequency determining elements,r selecting means for selecting any one of source for delivering energy limited to a frequency said elements, a work circuit including a power "determined by theV selected element, said work '7 nance of said work circuit to said frequency-determining element for terminating operation of said power means, and means for rendering said last mentioned means inoperative until completion of the first tuning cycle after said power means begins operation.

5. In automatic tuning apparatus,v in combination, a p-lurality of frequency determining elements, means for selecting any onev of said elements, a work circuit including a power source for delivering energy limited to a frequency determined by the selected element, said work circuit having a variable tuning instrumentality, power means for varying said instrumentality, resonance responsive means responsive to resonance of said work circuit to said frequency-determining element for normally controlling operation of said power means, and means for depriving said resonance means of control over said powermeans during the completion of the iirst tuning cycle l.

after said power means begins to operate.

6. In automatic tuning apparatus, in combination, a frequency determining element, a work circuitincluding a power source for -delivering energy limited to a frequency determined by said element, said work circuit having a variable tuning instrumentality, power means for varying said tuning instrumentality, energy responsive means comprising a rectier operativelyv associated with said work circuit, a resistance in circuit with said rectier, a control tube, connections for impressing the voltage drop through said resistance upon the input circuit of said control tube, whereby the plate current of said tube is reduced in response to resonance in said work circuit, a relay operated by the space current of said control tube, said relay being interposed in circuit with said power means to control the operation thereof, a second circuit for energizing said power means exclusive of said relay, a second relay connected in said second circuit, andv means for manually energizing said second relay, whereby said power means may remain energized independently of the action oi the rst said relay.

7. In automatic tuning apparatus, in combination, a frequency determining element, a work circuit including a power source for delivering enery limited to a frequency determined by said element, said work circuit having a variable tuning instrumentality, power means for varying said tuning instrumentality, energy responsive means comprising a rectier operatively associated with said work circuit, a resistance in circuit with said rectier, a control tube, connections for impressing the voltage drop through said resistance upon the input circuit of said control tube, whereby tlie plate current of said tube is reduced in response to resonance in said work circuit, a relay operated by the` space current of said control tube, said relay being interposed in circuit with said power means to control the operation thereof, a second circuit for energizing said power means exclusive of said relay, a second relay connected in said'second circuit, means for manually energizing said second relay, Whereby said power means may remain energized independently of the action of the first said relay, and a cam operated switch synchronized with said tuning instrumentality for opening the energizing circuit of said second relay atV a predetermined point in each tuning cycle.

8. In automatic tuning apparatus, in combina- Number area-ere v8 tion,y .a plurality of frequency ,determining elements, aV selecting Yswitchior selecting any one of said elements, a work circuit includingpower sourceforA delivering energy limited toza frequency determined-by the selected element, said Work circuit having va vvariable tuning-instrumentality, power means for varying said tuning instrumentality; energy responsive vmeans comprisingI a. rectifier operatively associated with said work circuit, a resistance in circuit with said rectifier, al control tube, connections for impressing the Voltage drop through vsaid resistance upon the input circuitof saidcontrol tube, whereby t-he plate current of `saidv tube is reduced in response toreso- Anance in said work circuit, a relay operated by the space current of said control tube, said relay being interposed in circuit withsaid power means to control the operationthereof, av second circuit for energizing said power means exclusive-of. said relay, a secondrelay connected in said circuit, means for manually energizing .said secondl relay, and means comprising a passing contact voperatively associated with said selecting switch.

9. In automatic tuning apparatus, in combination, a plurality of frequency determining elements, a selecting switch for selecting any one of said elements, a workv circuit including power source for delivering energy limited to a frequency determined by the selected element, said work circuit having a variable tuning instrumentality, power means for varying said tuning instrumentality, energy responsive means' comprising a rectier operatively associated withsaid workcircuit, a resistance in circuit with said rectier, a control tube, connections for impressing the voltage drop through said resistance upon the input circuit of said control tube, whereby the plate current of said tube is reduced in response to resonance in said work circuit, a relay operatedby the space current of said controlA tube, said relay being interposed in circuit withY said power means to control the operation thereof, a second circuit for energizing said power .means exclusive of saidrelay, a second relay .connected in said circuit, and means for manually energizing said second relay, said means comprising a passing Contact operatively associated with said selecting switch, anda cam operated switchl synchronized with said tuning instrumentality for opening the energizing circuit of saidsecondrelay at a predetermined point in each tuning cycle.V

HULBURT C. TITILE;

REFERENCES CITED The following references are of record inthe .File of this patent:

UNITED STATES PATENTS Name Date 1,907,965 Hansell May 9,1933 2,098,331 Bowman Nov. 9, 1937 2,193,843 Robinson Mar. 19, 1940 2,262,218 Andrews Nov. 11,1941 2,270,917 Appleton Jan'. 27, 1942 2,326,737 Andrews Aug.y 17, 1943 2,357,237 Thompson Aug. 29, A1944i 2,375,133 Polkinghorn May/1', 1945 OTHER REFERENCES Ser. No. 363,862, Dolle et a1(A. P. C.);, published May 25,1943.l 

